In general, it is preferable that when firing a guided projectile such as a missile, that the acquisition of the target occur as quickly and from as far away as possible. A missile system that acquires a target earlier does not require precise initial targeting or a launch platform in close proximity to the target. For military applications, these characteristics are especially important.
In order to detect the presence of a target, a missile system must be equipped with a sensor system. These sensor systems may detect radiation emanating from a target, determine the point of origin of that radiation, and direct the missile accordingly. The sensors can be sensitive to many different types of radiation emanating from a target including infra-red, visible light, radar, etc.
In many cases, the process of firing a missile includes a separate detection system that can detect the presence of possible targets. This auxiliary system may be a ground or vehicle-based radar station that is located in close proximity to the missile silo or magazine. The auxiliary detection system, upon detecting the possible presence of a target, maps out an uncertainty volume. This uncertainty volume describes a space—generally in the form of a cone emanating from the auxiliary detection system—in which the auxiliary detection system detects the presence of a possible target. The dimensions and orientation of the uncertainty volume are then transferred to the missile which, when fired, may scan the uncertainty volume for possible targets to attack. Depending upon the targeting requirements of the missile, the dimensions of the uncertainty volume can either be narrowed to increase the probability that the missile will find a target or broadened to ensure that a thorough search for targets is performed. If the missile itself does not efficiently detect targets, the initial uncertainty volume may be narrowed. However, if the uncertainty volume is too narrow it may not contain any targets. A broader uncertainty volume may be more preferable, but requires that the missile more efficiently and accurately search that uncertainty volume for a target.
One way to make a missile targeting system scan an uncertainty volume more efficiently is to increase the accuracy of its detection systems. Several methods have been used to increase the accuracy of missile detection systems. These include step-staring or tiling a square array of sensor detectors. This method includes recording data from the sensor system, moving the entire sensor system to record another image that does not overlap with the first, and then tiling the results to generate a larger data set. This method relies on the accuracy of each sensor pixel in the sensor array, potentially resulting in inaccurate data.
The sensor systems that missiles carry are not perfect and often contain defects such as dead, always-on, noisy or inaccurate sensor pixels. These inaccuracies result in a missile that is less likely to detect a probable target and more likely to detect a false target. They also severely limit the effectiveness of the step-staring or tiling method mentioned above. Several methods have been used in an effort to increase the fidelity of a missile's sensor systems. These include summing or averaging multiple frames recorded from the sensor system in an attempt to remove noise recorded by the sensor system. Although these methods are able to remove some noise from the system, they do not account for the problems associated with dead, always-on or inaccurate sensor pixels.